In a rotary grinder of this type, the material is divided and ground by a combination of shock and shearing effects between the rotating blades of the rotor and one or more blades fixed on a frame which surrounds the rotor.
A rotary grinder of this type is described in document FR 2 511 893. In this known grinder, the blades are disposed on the rotor so that, when one blade is working, the preceding one serves as stop for the material pushed by the working blade, so as to provoke a screw effect which imparts to the material a displacement having a component parallel to a generatrix line of the rotor. More particularly, in the document mentioned above, the blades mounted on the rotor are disposed in two antagonistic series of blades in staircase form so that these blades enter into action successively, each series beginning at one end of the rotor and terminating in the central region thereof, so that the resulting Archimedean screw effect acts on the material in two opposite directions going from the two ends of the rotor up to its central region. The aim of this document is to detach all material from the end zones in which are located the bearings which support the rotation shaft of the rotor.
However, Applicants have observed that, although there was effectively a clearing of the end zones corresponding to the location of the bearings, there was, on the other hand, an accumulation of the materials to be ground towards the central part of the rotor, such an accumulation being detrimental to the correct homogeneous functioning of the grinder.
It is an object of the present invention to propose a rotary grinder employing blades, which does not present the drawbacks set forth hereinabove, namely of which the arrangement of the blades makes it possible not only to avoid an accumulation of materials in the end zones in which are located the bearings supporting the rotation shaft of the grinder, but also to obtain a perfect operational homogeneity over the whole length of the rotor.
This object is perfectly attained by the rotary grinder of the invention, which is a rotary grinder employing blades, comprising, in known manner, a substantially cylindrical rotor on the periphery of which is mounted, along certain regularly spaced apart generatrix lines, a plurality of identical blades of small length with respect to the length of the rotor.
According to one characteristic feature, the blades are disposed at a rate of one blade per generatrix line and so that two blades located on adjacent generatrix lines present, longitudinally therebetween, a distance which is slightly shorter than, equal to or greater than a length of blade. When a given blade is working, the preceding blade does not serve as stop for the material pushed by the working blade and consequently, the screw effect, which is precisely sought by document FR 2 511 893, is no longer obtained.
The grinder according to the invention preferably comprises n groups of blades having strictly the same arrangement, regularly distributed over the whole periphery of the rotor. The number of groups n is preferably equal to three. In that case, each group of blades occupies a third of the periphery of the rotor.
According to a preferred embodiment of the grinder of the invention, each group of blades comprises at least five blades of which the arrangement, shown flat, is substantially in the form of a W.
If it is question of a grinder of which each group comprises six blades, the arrangement, shown flat, is as illustrated in FIG. 3 of the accompanying drawings. If it is a grinder of which each group comprises eight blades, the arrangement, shown flat, is as illustrated in FIG. 4.